The present invention relates to an apparatus for determining deviations from a circular form in a dynamically balanced part, in particular, a steel pipe. The apparatus includes a spindle which can be set in approximate alignment with the axis of the unit being tested and an interval sensor mounted for rotation around an axis of the spindle axis for radially sensing a circumferential surface of the unit under test.
When laying steel pipe lines for natural gas and the like, the individual pipe sections are welded to one another directly in situ. In order to be able to properly draw the welds, the end regions of the pipe sections cannot have any inadmissibly great deviations from a circular form such as being out-of-round, outward dents, inward dents or weld bosses or bulges. Since such unallowed deviations from the circular form are frequently not noticed until the weld is being formed, they can lead to considerable difficulties at the construction site. In order to avoid these difficulties that can be overcome only with difficulty at the construction site, the end regions of the pipe sections to be welded to one another must have been subjected to a prior roundness check so that the pipe sections having unallowed deviations from a circular form can be either reworked to provide the desired circular form or set aside.
For a roundness check or, respectively, for determining deviations from a circular form in a dynamically balanced part, it is known to employ a so-called spindle measuring device wherein a spindle must first be set in alignment with the axis of the unit under test. The sensing then occurs radially wherein either the unit under test is rotated or the caliper is rotated. The excursion of the measuring sensor is then pneumatically or electrically amplified and is then recorded with a polar recorder. The deviations from the circle are then determined from the polar diagram as the difference in the diameters of two concentric circles between which the circumferential line of the polar diagram lies. This deviation as well as explanations of different ways of determining it are set forth in Lexikon der Fertigungstechnik und Arbeitsmaschinen, Deutsche Verlags-Anstalt, Stuttgart, 1968, Vol. 9, Pages 213-214.
Since an eccentric setting of a spindle is expressed as an error or deviations from a circular form that is being tested, the spindle for the known measuring devices for roundness checks should be set in alignment with the axis of the unit under test as precisely as possible. When testing hollow cylindrical parts such as steel pipes and the like, however, the spindle can only be approximately aligned to the axis of the unit under test so that the spindle adjustment implementated with justifiable outlay allows only imprecise measurements of the deviations from a circular form.